| 摘要: | 隨著物聯網技術在全球快速的擴展，在非地面網路中實現高效連接變得更加重要。非地面網路(Non-terrestrial Networks, NTNs)的物聯網(Internet of Things, IoT)技術通常遵循第三代合作夥伴計畫(The Third Generation Partnership Project, 3GPP)的規範，而3GPP致力於建立全球統一的窄帶物聯網(Narrowband Internet of Things, NB-IoT) 運作標準。本文研究了一種統一的隨機存取(Random Access, RA)程序，使NB-IoT協議能夠在無需全球導航衛星系統(Global Navigation Satellite System, GNSS) 連接的情況下，在NTN與地面網路(Terrestrial Networks, TN)之間實現無縫運作。為了保證高精度和向後相容性，該方法在窄頻物理層隨機存取通道(Narrowband Physical Random Access Channel, NPRACH)接收器上採用了共同多普勒頻移的預補償與後補償。同時針對衛星上NPRACH接收器，還利用了共用傳播延遲進行預先定時提前(Pretime Advance, Pre-TA)與隨機存取機會(Random Access Opportunity, RAO)的延後處理。
本文提出了一種犁耙式接收器(rake receiver)架構，在每個犁耙式分支上配置一組訊符等級關聯器(Symbol-Level Correlator, SLC)，以在完成NPRACH前導碼檢測後，對剩餘頻率誤差(Residual Frequency Error, RFE)與剩餘時序誤差(Residual Timing Error, RTE)進行聯合最大概似估計(Joint Maximum Likelihood Estimation, JMLE)。該技術利用高速率訊號處理，在時域對接收訊號進行降取樣(Decimation)以降低後續運算複雜度，並在頻域進行上取樣(Upsampling)以提升餘頻率誤差估計的精確度。透過相干累加訊符等級關聯器輸出的平方幅度，可進一步提升訊號對干擾與雜訊比(SINR)。本文所提出之方法具備高度彈性與實用性，不僅能在超越單一子載波間距與單一符號持續時間的範圍內精確估計剩餘時序誤差與剩餘頻率誤差，還能達到子載波間距與符號持續時間的分數級精度。模擬結果證實了此方法的有效性。
;For rapid deployment, Internet of Things (IoT) technology operating in nonterrestrial networks (NTNs) usually follows 3GPP specifications. The 3GPP aims to establish unified specifications for global narrowband IoT (NB-IoT) operations. This article investigates a unified random access (RA) process for an NB-IoT protocol seamlessly operating between NTNs and terrestrial networks without global navigation satellite system (GNSS) connectivity. For high accuracy and backward compatibility, the common Doppler shift is employed for preand post-compensations at a narrowband physical RA channel (NPRACH) receiver; meanwhile, a common propagation delay is employed for pretime advance (Pre-TA) and RA opportunity (RAO) postponement at the NPRACH receiver on the satellite. This study proposes a rake receiver to convey a bank of symbol-level correlators (SLCs) on each arm for joint maximum likelihood estimation (JMLE) of residual frequency error (RFE) and residual time error (RTE) after narrowband physical random access channel (NPRACH) preamble detection is completed. The proposed technique exploits multi-rate signal processing to decimate (i.e., downsample) the received signal for reducing subsequent computational complexity and to interpolate (i.e., upsample) in the frequency domain to enhance the accuracy of RFE estimation. Coherent accumulation of the squared magnitudes of SLC outputs further improves the signal-to-interferenceplus-noise ratio (SINR). The proposed approach offers flexibility and practicality, enabling highly accurate estimation of RFE and RTE over extended ranges beyond one subcarrier spacing and beyond one symbol duration, respectively, while achieving precision at the fractional levels of a subcarrier spacing and a symbol duration. Simulation results confirm effectiveness of the proposed technique. |
